Retorting oil shale with special pellets and supplemental deposition

ABSTRACT

1. IN A METHOD FOR RETORTING CRUSHED OIL SHALE CONTAINING CARBONACEOUS ORGANIC MATTER AND MINERAL MATTER WHEREIN OIL SHALE IS RETORTED BY CONTACTING SAID OIL SHALE WITH HOT PELLETS IN A RETORT ZONE TO GAS AND OIL PRODUCTS, A COMBUSTIBLE DEPOSITION ON SAID PELLETS, AND PARTICULATE SPENT SHALE, SAID PELLETS HAVING BEEN HEATED IN A PELLET DEPOSITION BURNING ZONE TO A RETORT ZONE INLET TEMPERATURE OF BETWEEN 1000*F. AND 1400*F. MAINLY BY COMBUSTION OF A COMBUSTIBLE CARBON-CONTAINING DEPOSITION ON SAID PELLETS, SAID PELLETS BEING IN AN AMOUNT SUFFICIENT TO PROVIDE AT LEAST 50 PERCENT OF THE HEAT REQUIRED TO VAPORIZE A MAJOR PORTION OF THE CARBONACEOUS MATTER FROM SAID OIL SHALE AND TO HEAT SAID CRUSHED OIL SHALE FROM ITS RETORT ZONE INLET TEMPERATURE TO A RETORT ZONE OUTLET TEMPERATURE OF BETWEEN 800*F. AND 1150*F. AND WHEREIN SAID GAS AND OIL PRODUCTS ARE SEPARATED AND RECOVERED, THE IMPROVEMENT COMPRISING PASSING AT LEAST A PORTION OF SAID PELLETS FROM SAID SEPARATION ZONE TO A SUPPLEMENTAL DEPOSITION ZONE AND AT THE SAME TIME PASSING AT LEAST A PORTION OF SAID OIL PRODUCTS TO SAID SUPPLEMENTAL DEPOSITION ZONE INTO CONTACT WITH SAID PELLETS IN SAID SUPPLEMENTAL DEPOSITION ZONE TO DEPOSIT ADDITIONAL COMBUSTIBLE CARBON-CONTAINING DEPOSITION ON SAID PELLETS IN SAID SUPPLEMENTAL DEPOSITION ZONE, AND THEREAFTER PASSING SAID PELLETS WITH SAID ADDITIONALLY DEPOSITED COMBUSTIBLE DEPOSITION FROM SAID SUP PLEMENTAL DEPOSITION ZONE TO AID PELLET DEPOSITION BURNING ZONE.

0. K. WUNDERLICH ETAL v ,8

RETORTING OIL SHALE WITH SPECIAL PELLETS AND SUPPLEMENTAL DEPOSITION Filed Oct. 26, 1973 2 Sheets-Sheet 2 3,841,994 RETORTING OIL SHALE WITH SPECIAL PELLETS AND SUPPLEMENTAL DEPOSITION Donald K. Wunderlich and James L. Skinner, Richardson, Tex., assignors to Atlantic Richfield Company, Los Angeles, Calif.

Continuation-impart of application Ser. No. 304,074, Nov. 6, 1972, which is a continuation-in-part of application Ser. No. 284,288, Aug. 28, 1972, both now abandoned. This application Oct. 26, 1973, Ser. No. 410,098

Int. Cl. Cb 53/06 U.S. Cl. 20811 43 Claims ABSTRACT OF THE DISCLOSURE Hot special pellets are cycled to a retort zone to retort crushed oil shale thereby producing gas and oil products, a combustible coke-like deposition on the pellets, and particulate spent shale. The main source of heat for retorting is derived from burning a combustible deposition formed on the pellets during the process. The combustible deposition is comprised of the combustible deposition formed during retorting and an organic substance formed during a postretort supplemental deposition stage. The supplemental deposition stage is carried out by contacting at least a portion of the pellets with at least a portion of the oil products after the pellets have been separated from substantially all of the spent shale smaller than the pellets. Preferably, the supplemental deposition stage involves thermal cracking or stabilization of some of the oil products. The postretort supplemental deposition stage provides flexibility over the total deposition and allows more leeway in operation of the retort zone. The special pellets are characterized primarily by their effective surface area, size, and quantity relative to the oil shale.

CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of copending application 304,074, filed Nov. 6, 1972, entitled Retorting Oil Shale With Special Pellets and Supplemental Deposition, now abandoned, which was a continuation-inpart of copending application Ser. No. 284,288, filed Aug. 28, 1972, entitled Retorting of Oil Shale With Special Pellets, now abandoned. All of said applications have been filed by the same inventors as this application and owned by a common assignee.

BACKGROUND OF THE INVENTION This invention relates to a process for retorting the solid carbonaceous organic matter in crushed oil shale. In the process, special heat-carrying pellets are cycled in a particular Way to a retort zone and thence at least some of the pellets are passed through a supplemental deposition stage to form additional combustible substance on the pellets.

As a preliminary stage in the production of petroleum oils and gases, the solid carbonaceous organic solid matter or kerogen in oil shale is pyrolyzed or retorted. In an overall commercial operation, the products or yield of retorting are processed in additional stages for example, solids separation, condensation, fractionation, coking, hydrogenation, and the like, depending on the types of marketable products being produced. Many processes have been suggested for the retorting stage of a commercial operation. The term retorting denotes thermal conversion of kerogen or organic matter to oil vapors and gas thereby leaving solid particulate spent shale and includes separation of the oil vapors and gas from the spent shale. The spent shale contains residual carbonaceous organic matter and matrix mineral matter.

Frequently, the yields of various processes are com- United States Patent O 3,841,994 Patented Oct. 15, 1974 pared with Fischer Assay yields. For a description of the Fischer Assay refer to Method of Assaying Oil Shale by a Modified Fischer Retort by K. E. Stanfield and I. C. Frost, R. I. 4477, June 1949, US. Department of Interior.

When the kerogen is retorted, a normally gaseous fraction, a normally liquefiable vaporous fraction, and an organic residue are formed. The product distribution between gas, liquid, and residue is indicative of the distribution of the various boiling point fractions in the liquid product. It is highly desirable to obtain a liquid product that is directly adaptable to prerefining and avoids or lessens the amount of residue or 975 F. plus fraction that must be subjected to coking or other similar treatments. In many retorting processes control over the product distribution is virtually absent, and in others, any attempt to reduce the need for coking and the like by altering the boiling point distribution in the liquids either results in too much unusable material, or too much gas product, or too much organic residue, or any combina tion thereof, which in turn eventually result in a loss of liquid oil yield. Any advantage obtained by attempting to control product or residue conversion is frequently offset by undesirable shifts in other process variables or results. In addition, the kerogen content of the oil shale inherently or naturally fluctuates between rich and lean and many processes are not sufliciently flexible to control product distribution when the kerogen content varies.

Some advances to more flexible and efficient control over the products of retorting and of other variables have been made by using solid heat-carrying bodies which exhibit good heat transfer properties and supply the heat needed for retorting with a reduction in process problems. In such processes, the heat-carrying bodies and the oil shale feedstock are intermixed thereby retorting oil vapors and gases from the feedstock. The heat-carrying bodies are usually heated in a separate heating zone by burning combustible fuel material, such as heavy resid or natural gas. But in general, this method of heating necessitates additional equipment and creates additional handling problems.

Others have proposed cycling the spent shale and supplying some of the heat by burning the residual carbonaceous organic matter or solid organic char developed in the retort zone, or cycling catalyst particles and supplying some of the heat by burning carbon deposited on the catalyst (for example, US. Pat. 3,281,349). In this latter process, the surface area of the catalyst particles is not specified. Some types of catalyst particles frequently have high surface areas which result in loss of valuable liquid product and excessive gaseous product, excessive residue, excessive heating of the catalyst during burning, loss of valuable heat values, higher oxygen demands, and other disadvantages.

In addition, a large amount of fine (e.g. minus 14 US. Standard Sieve size) particulate spent shale is usually present during burning and reheating. This spent shale contains organic carbon and increases oxygen demands, causes loss of useful heat values, and adversely enlarges the size of equipment. Fine spent shale or other materials also interfere with control of the burning and other stages of the process and create many other problems especially when the entrained spent shale is smaller than other heatcarrying bodies. Moreover, the presence of appreciable amounts of fine spent shale severely limits the type of equipment which can be used for burning the residue. Generally, burning in the presence of fine spent shale requires the use of lift pipes. If air is used for lifting, the burning could entail a large excess of oxygen which could rapidly burn the organic matter and create disadvantages in the process of this invention.

Copending application Ser. No. 410,200, which is a continuation-in-part of application 284,288, which is in corporated herein, provides a process for retorting oil shale using hot special pellets in a way which regulates the amount of combustible organic carbon deposition formed on the pellets during retorting of oil shale and improves the recovery of useful components and liquid product distribution. The deposition acts as a principal source of fuel for heating the pellets. The process relies on the interrelation between the surface area of the pellets and other conditions and variables; however, additional flexibility in the operation of the process, especially the retorting zone, is desired primarily because it has been found that the retorting stage of the process requires constant control and adjustment and altering one variable effects other variables and results, and because it is desirable at times to operate the retort zone under conditions such that the deposition formed on the pellets during retorting of the oil shale is not sufi'icient to supply a major portion of the fuel required for heating the pellets. At other times, it is desirable to supply more combustible deposition on the pellets without altering the operating characteristics of the retort zone. Such conditions could arise, for example, when a vein of lean oil shale is encountered and the design and size of the retorting equipment are such that it Would be undesirable or ineflicient to adjust operations to the lean shale. There are other similar occurrences or objectives which arise during retorting of shale. When such occurrences take place or when objectives change or fluctuate, more process flexibility is advantageous. Briefly, therefore, a principal object of this invention is to provide greater flexibility and adaptability to a retortng process of the type disclosed in copending application Ser. No. 410,200, filed Oct. 26, 1973.

SUMMARY OF THE INVENTION In a retorting process, crushed carbonaceous solid organic matter is retorted to gas, oil vapors, and combustible residue with special heat-carrying pellets in a manner which increases the utility of all three retort products and provides greater useful recovery of the residue that is normally formed when oils are retorted, cracked, or vaporized. Greater useful recovery of this residue reduces the need for gaseous or liquid fuels which are normally required in the production of syncrude from solid carbonaceous materials and of producing with improved flexibility and adaptability. The process cycles special hot heat-carrying pellets in a way which produces a combustible carbon-containing deposition on the pellets and renders the deposition more useful as a fuel for heating the pellets that are used to retort oil shale. In the process, some or all of this deposition is burned in a pellet deposition burning zone to heat or reheat the pellets. Some of this combustible deposition is formed or adsorbed on at least a portion of the pellets during a postretort supplemental deposition stage in which at least a portion of the vaporous, or condensed, or condensed and fractionated retort products are adsorbed or cracked, or both, on at least a portion of the pellets to deposit additional combustible deposition on the pellets thus exposed. Preferably, the supplemental deposition stage is carried out under conditions such that the retort products are thermally cracked or stabilized and under conditions such that less than ten percent by weight of combustible deposition is formed on the pellets during passage through the supplemental deposition stage. Also it is preferred that the space velocity in the supplemental deposition zone be between 0.25 and 2.0. The supplemental deposition stage is carried out after the pellets have been passed through the retort Zone. In the retort zone, some coke-like combustible deposition is formed on the pellets. The combustible deposition formed on the pellets in the supplemental deposition stage, therefore, acts as an addition to the deposition formed during the retort stage, thereby increasing the total amount of fuel deposition. Since this portion of the total combustible deposition is formed on the pellets after the retorting stage of the process, the retorting stage may be operated under conditions which decrease the amount of deposition formed during retorting, or the percentage of deposition by weight on the pellets. This supplemental deposition stage, therefore, provides greater flexibility to the overall process, especially the retorting stage. The amount of deposition formed on the pellets in the retorting stage of the process is preferably less than 1.5 percent by Weight per pass through the pyrolysis retort. As a side advantage, the supplemental deposition stage may be carried out in such a Way as to thermally crack or stabilize products and at the same time place the combustible coke that is normally formed during thermal cracking in a better position to be used as fuel for reheating the pellets to retort oil shale. Thermal cracking has the further advantage of tending to limit the combustible deposition to coke-like residues which are far less valuable than the other oil products. The supplemental deposition stage provides additional flexibility and adaptability to the retorting process since the operator has the choice of subjecting all or only a part of the retort products to such supplemental stage. The quantities of pellets or products, or both, so treated may be varied to coact with changes in other variables especially the organic content of the raw shale and the desired product yields. Still further advantages are available in that the burning of the combustible deposition and the cycling of the pellets tends to reduce the effective surface area of the pellets and the amount of coke-like deposition formed during the retorting stage. The rate of change in surface area is not constant and tends to approach an asymptotic or equilibrium value which is established by the nature of the pellets and the process conditions. The flexibility provided by the supplemental deposition stage can be used to compensate for such changes in surface area or to provide more uniform operating conditions for the retort zone.

The special pellets are comprised of particulate or divided solid heat carriers whose physical properties and characteristics, especially surface area, size, shape, temperature, and amount, coact with other variables to control the amount of organic combustible deposition formed on the pellets during the process, especially during the retorting stage, and to accomplish the other objectives and advantages of the process.

In the process, mined oil shale which contains solid carbonaceous organic matter and other mineral matter and which has been crushed and may have been preheated is pyrolyzed or retorted in a retort zone with the special hot heat-carrying pellets at a temperature and in an amount suflicient to provide at least 5-0 percent of the sensible heat required to retort oil shale. Retorting of the shale produces gases and oil vapors which are recovered and particulate spent shale. Retorting also tends to deposit a carbon-containing deposition on the special pellets.

After retorting the oil shale, at least percent of the total particulate spent shale and at least percent of the particulate spent shale smaller than the pellets are separated from the pellets prior to the supplemental deposition stage and to burning of the combustible deposition on the pellets. Pre-separation of the spent shale avoids wasteful deposition of valuable organic products on the spent shale and avoids the problems caused by fine matterduring burning. One way to accomplish this separation is to first screen large spent shale and agglomerates from the pellets and thereafter subject the pellets and spent shale to gas elutriation with a uoncombustion supporting gas. A Way of enhancing the degree of total separation is to control the sphericity factor of the pellets to at least 0.9, or to crush the raw oil shale to a smaller than normal size, that is, to minus 6 US. Sieve Series size.

After separation of the spent shale, at least a portion of the separated pellets and at least a portion of the product are passed to a supplemental deposition zone where the product contacts the pellets and some of the product is either adsorbed on the pellets or some of the product is thermal cracked. In either case, a combustible organic carbon-containing deposition is deposited on the pellets. The pellets bearing the combustible deposition are then passed to pellet deposition burning zone where at least a portion of combustible deposition is burned to heat the pellets.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, FIG. 1 is a schematic flowsheet of the process of this invention; and

FIG. 2 is a partly schematical, partly diagrammatical flow illustration of a system for carrying out a preferred sequence of the process of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION A process for retorting crushed oil shale containing carbonaceous organic matter and other mineral matter is described in general terms having reference to FIG. 1 and in more particular terms having reference to FIG. 2.

Raw or fresh oil shale which has been mined and pulverized, crushed or ground for the most part to a predetermined maximum size for handling in a retorting system by any suitable particle diminution process is fed directly from a crusher or from a hopper or accumulator by way of shale inlet line 11 into retort zone 13. At the same time, special heat-carrying pellets substantially hotter than the shale feed are fed by gravity or other mechanical means to the retort zone by way of pellet inlet pipe 15. The pellets and shale feedstock could be fed to the retort zone by way of a common retort zone inlet.

Crushing of the raw mined shale expedites more uni form contact and heat transfer between the shale feedstock and hot pellets. In normal practice, the degree of crushing is simply dictated by an economic balance between the cost of crushing and the advantages to be gained by crushing when retorting the kerogen from the shale. Generally the shale feedstock is crushed to about one-half inch and no particular care is taken to produce or restrict production of finer material. In this process, crushing has a special purpose and aids in a preburn separation step. In one embodiment, for reasons which will be hereinafter shown and despite the added costs and standard practice, the mined shale is crushed to a substantially finer size wherein at least 95 percent by weight of the crushed oil shale will pass through a US. Sieve Series size 6 screen.

The crushed oil shale may or may not be preheated by direct or indirect heat from any source including indirect heat exchange with pellets or flue gases generated during this retorting process. If the shale feedstock is preheated, the temperature of the feedstock will not exceed 600 F. The shale feedstock will usually be fed by way of a metered weight controller system for reasons hereinafter made apparent and which may include a preheat and/or gas lift system. The preferred system for preheating the raw shale is to lift the shale in lift pipes with the hot flue gases generated in the combustion phase of the process.

The hot special heat-carrying pellets are especially characterized by having a principal size during use of between approximately 0.055 and 0.5 inch, and preferably between 0.055 and 0.375 inch, and a surface area during use of between 10 and 150 square meters per gram. The surface area is the average effective surface area of the pellets as they enter the retort zone. The surface area may be determined by the conventional nitrogen absorption method. In one embodiment of the process of this invention, the surface area of the pellets on a gram basis is between 10 and 100 square meters. The importance of surface area is hereinafter discussed in detail. The heatcarrying pellets are at temperatures ranging between heat required to heat the shale feedstock from its retort zone feed temperature to the designed retort temperature. The retort zone feed temperature is the temperature of the oil shale after preheating, that is, the temperature of the shale upon entry into the retort. The average retort temperature ranges between about 850 F. and 1200 F. de-

ending on the nature of the shale feedstock, the pelletto-shale ratio, the type of product distribution desired, heat losses, and the like. The relative mass and size of the pellets are selected in a manner hereinafter set forth which facilitates separation of the pellets from spent shale, controls the amount of combustible carbon-containing deposition deposited on the pellets, optimizes other facets of the retorting process, and makes allowance for wear or size reduction of the pellets as they are cycled and recycled through the retorting process.

The term pellets refers to subdivided or particulate bodies. A majority of the bodies have the characteristics and pro erties herein required and which are composed of the same or dissimilar materials having the specified surface area and strength and of irregular shape, cylindrical shape, approximately oval or spherical shape, or purely spherical shape. The preferred pellets have a sphericity factor of at least 0.9 which, in addition to the usual advantages of facilitating movement of the pellets through the retorting process and of providing optimum solid-to-solid heat transfer and contact between the pellets and oil shale feedstock, has an advantage particularly useful in separating the pellets from other solids produced in the process as hereinafter set forth. The sphericity factor is the external or geometric surface area of a sphere having the same volume as the pellet divided by the external surface area of the pellet.

The pellets are made up of materials, such as, alumina or silica alumina, which are not consumed in the process and which are subdivided or particulate matter having significantly high internal surface area, but not excessively high. The pellets are sufficiently wear or breakage resistant and heat hesistant to maintain enough of their physical characteristics under the conditions employed in the process to satisfy the requirements herein set forth, to effect retorting of the oil shale, and to permit controlled burning of a carbon-containing deposition formed on the pellets during the process. More specifically, the pellets do not disintegrate or decompose, melt or fuse, or undergo excessive surface area reduction at the temperatures encountered during such burning and the thermal stresses inherent in the process. The pellets will, of course, undergo some gradual wear or size reduction.

As will be shown, the size of the pellets is related to the other variables and to the preburn spent shale separation step of this process. The original or fresh pellets are generally comprised of particulate sensible heat carriers in a size range between about 0.1 inch and 0.5 inch, and preferably between 0.1 inch and 0.375 inch, and are for the most part maintained during use at a plus 14 US. Sieve Series Screen size, that is, approximately about 0.055 inch or greater. Finer pellet grain sizes are undesirable in the process of this invention.

Suitable pellet materials are also found in cracking catalyst; however, the retorting process of this invention is not to be considered as relying on active catalytic sites. Many catalysts have surface areas far in excess of the maximum surface area of square meters per gram provided in this process. For example, some silica alumina catalysts that may have a surface area ranging between 180 and 700 square meters per gram. As will hereinafter be discussed and as indicated by the trend shown in Table 1, high surface areas tend to cause too much combustion carbon-containing deposition or coke-like residue being deposited in the retort zone.

Active catalytic sites tend to have effects similar to excessively high surface areas. As a result, in this process, although cracking catalysts may be used, it is preferred that the pellets bear no added active acid catalytic catalyst sites or the like when the pellets are added to the retort zone. What is preferred are pellets that have the size and surface area limitations herein set forth. Of course, the retorting phase of this process and the subsequent deposition combustion phase could be conducted with a catalyst with some loss of flexibility in such a manner as to kill or limit active catalyst sites and limit or destroy excessive available pellet surface area; but it is preferred that the pellets not hear such sites and have or rapidly develop the prescribed surface area range naturally. Thus, the pellets could be comprised of particulate or subdivided matter, for example, catalyst particles, composed or manufactured of materials which can be treated to reduce their surface area and which are of appropriate size, but which originally had a surface area in excess of 150 square meters per gram, and which have been treated to reduce the effective surface area to less than 150 square meters per gram. An originally high surface area can be permanently reduced by methods similar to the way that catalyst particles lose their eifective surface area as they age when used in catalytic cracking or hydrogenation units, or by subjecting the particles to rapid or prolonged aging at temperatures and fluid pressures sufiicient to reduce the surface area of the particles. A preferred way to cause this reduction in surface area is to subject the particles to temperatures above 1400 F. and in the presence of steam at pressures between 0.5 and 7 atmospheres until the surface area is reduced to the desired level. By way of illustration, it has previously been reported in accelerated aging experiments that by subjecting a silica-alumina catalyst to one atmosphere of steam for one hour at 1585 F. the surface area was reduced from about 180 square meters per gram to about 95 square meters per gram, and in a similar experiment at 1432 F. the surface area was reduced from about 400 square meters per gram to about 100 square meters per gram. The high surface area particulate matter thus treated may originally have been comprised of high surface area particles with active acid catalytic sites. In such case, the particles could also be treated to deactivate their active acid catalytic sites by subjecting them to conditions and chemicals known to poison or kill such active acid catalytic sites, for example, by treatment with sodium bicarbonate, sodium hydroxide, or sodium carbonate.

The retort zone is any sort of retort which causes intimate contact or mixing of the crushed oil shale and pellets. The preferred retort is any sort of horizontal or inclined retorting drum that causes the oil shale and pellets to undergo a tumbling action. This sort of retort is herein referred to as a rotating retort zone. This type of retort zone is quite flexible over a wide range of conditions and has the advantages of causing rapid. solid-tosolid heat exchange between the pellets and shale feedstock thereby flashing and pyrolyzing the oil and gas vapors from the shale in a way which allows the vapors to separate from the solids without passing up through a long bed of solids and which minimizes dilution of the product vapors by extraneous undesirable retorting gases; of allowing for a high shale throughout rate at high yields for a given retort volume; of providing for greater control over residence time; of aiding in preventing overcoking and agglomeration of the pellets and shale; of facilitating formation of a more uniform controlled amount of combustible carbon-containing deposition or coke-like deposition on the surface area of the pellets;

and of causing How of the pellets and shale through the retort zone in a manner which aids in eventual separation of the pellets from the spent shale. The amount of deposition deposited on the pellets during the retorting stage of the process is an important feature and will be discussed later in more detail. The retorting process is carried out in concurrent or parallel flow fashion with the hot pellets and the raw shale feedstock being fed into the same end of the retort. The retort zone may be maintained under any pressure which does not hamper efiicient operation of the retort, interfere with production of valuable retort vapors, or cause excessive deposition or residue on the pellets. Generally, pressurization of the pyrolysis or retort zone causes considerable diiiiculties especially if a rotating retort zone is used. The pressure employed is, therefore, generally the autogenous pressure.

In the retort zone, the hotter pellets and cooler crushed shale feedstock are admixed and intimately contacted almost immediately upon being charged into the retort zone. The shale particles are rapidly heated by sensible heat transfer from the pellets to the shale. Any water in the shale is distilled and the kerogen or carbonaceous matter in the shale is decomposed, distilled, and cracked into gaseous and condensable oil fractions, thereby forming valuable vaporous effluents including gas, oil vapors, and superheated steam. Pyrolysis and vaporization of the carbonaceous matter in the oil shale leaves a particulate spent shale in the form of the spent mineral matrix matter of the oil shale and relatively small amount of unvaporized or coked organic carbon-containing material.

As the aforementioned vaporous effluents are formed, a combustible organic carbon-containing deposition or coke-like residue will be formed or deposited on the pellets if the effective surface area of the pellets has not already been covered with all of the deposition that it can sustain. The variables and stages of this process as herein set forth are related in a manner which controls the total amount of combustible carbon-containing deposition deposited during the process and the amount deposited during the retorting stage of the process. The total amount of combustible deposition formed or deposited on the pellets upon one passage through the process is suflicient upon combustion to provide at least 50 percent of the heat required to reheat the pellets. The preferred amount of combustible deposition deposited on the pellets during the retorting stage is on an average less than 1.5 percent by Weight of the pellets and the preferred range is between 0.8 and 1.5 percent. Basically, these controls are critical in two respects. First, the total amount of combustible deposition on the pellet is important since as will hereinafter be shown this combustible deposition is burned in a controlled manner to generate a major portion of the heat necessary for heating the pellets to carry out the retorting phase of the process. Second, the total amount of combustible deposition especially the coke-like residue formed during retorting affects the relative yields of gas and condensable or final liquefied products. This in turn affects the distribution of various boiling point fractions in the liquefied products. The total amount of combustible organic carbon-containing deposition deposited is basically controlled in this process by the retorting stage of the process and by a supplemental deposition stage as hereinafter described which are in turn controlled by the interrelation of several variables, such as pellet-to-shale ratio, pellet size and surface area, the percentage of the pellets passed through the supplemental deposition stage, the space velocity and types of products passed through the supplemental deposition stage relative to the percentage of pellets passed through this supplemental stage, the pellet holding time in the supplemental deposition stage, pellet inlet temperatures to the supplemental deposition stage and to the retort zone, and the outlet temperatures of the supplemental deposition stage and the retort zone. Additional operating leeway or control over both the total amount of combustion deposition deposited on the pellets and the amount of deposition deposited on each pellet may be obtained by residence time or throughput rate in the supplemental deposition stage and in the retort zone, partial or complete combusion of the combustible deposition, control of combustion time or amount of oxidizing gas used during burning, the noncatalytic characteristics of the pellets, and the size of the pores at the surface of the pellets. As can be readily seen by this description of the process, the degree of regulation or control provided by a single variable is never independent and the flexibility of regulation varies with the type of variable.

The pellet surface area is considered one of the most important variables. The effect of pellet surface area is illustrated by the test results set forth in Tables 1, 2, and 3. The effect of pellet surface area on the amount of combustible carbon-containing deposition formed on pellets and on the distribution of carbon deposition between the pellets and spent shale is illustrated in Table l. The effect of pellet surface area on liquid product distribution when a modified Fischer retort was used is illustrated in Table 2. The effect of pellet-to-shale ratio and, therefore, the total surface area of the pellets is illustrated in Table 3. The total surface area is determined by the surface area per gram of pellets and the total pellet weight which in turn is controlled by the pellet-to-shale ratio and shale throughput rate. The results illustrated in these tables lead to several conclusions. First, if the surface area exceeds 150 square meters per gram, too much coke-like deposition may be produced on the pellets during the retorting stage of the process when the pellet-to-shale ratios specified herein are used. This in turn indicates an undesirable or excessive shift toward gaseous products in the retort zone.

If the surface area of the pellets is less than ten square meters per gram, either too little total coke-like deposition will be formed in the retort zone or the burning of the deposition will not be suflicient to provide a major portion of the heat required to heat the pellets to the desired temperature and to carry out the retorting phase of this process. This would necessitate the use of supplementary fuels and as stated previously, this has significant disadvantages to the objects of this process.

TABLE 1.EFFECT OF PELLET SUR- FACE AREA ON CARBON DEPO- SITION Wt. percentage of carbon on- Residual Pellet area, mJ/g. Pellets shale TABLE 2.EFFECT OF PELLE'I SURFACE ON LIQUID PRODUCT DISTRIBU- Pellet area Product N boiling range pellets 47 mfi/g. 96 mJ/g.

15040() F 27% 34% 400700 F 46% 48% 700900 F 22% 14% 900 F.+ 19% 4% *Pelle'tzShale ratio=2:1

As illustrated in Tables 2 and 3, the effective surface area of the pellets and the pellet-to-shale ratio in the retort zone affect liquid product distribution of the products from the retort Zone. Increasing the surface area and the pellet-to-shale ratio tends to decrease the yield of condensable product vapors and increase production of gases. As mentioned previously, one objective of this process is to optimize the balance between useful deposition which acts as a fuel and oil products. This objective places restrictions on the retorting stage which restrictions are partially alleviated in this process by the flexibility over the total combustible deposition that is provided by supplemental deposition stage. As a result, the operator has additional leeway when selecting the pellet-toshale ratio and the original surface area of the pellets. All variables considered, it has been concluded that an original pellet surface area between 10 and 150 square meters per gram is acceptable with the range of 10 to being preferred and that operating with a pellet-toshale ratio between 0.5 and 3.5 is feasible with a ratio between 1 and 3 being preferred.

As illustrated in Table 1, of particular additional significance is the fact that a substantial portion of the combustible deposition on the pellets comes from the residual carbonaceous material that would normally be left on the spent shale. In other words, the organic carbon material that is normally left on the spent shale divides itself between the pellets and the spent shale. This process, thereby, recovers residue that would normally be lost with the spent shale. The recovered deposition is then made useful as fuel for heating the pellets.

The mixture of pellets and shale moves through the retort zone toward retort exit 17 and the gaseous and vaporous efiluents containing the desired hydrocarbon values separate from the mixture. Since there is no need to use carrier, fluidizing, or retorting gases in the retort zone, the gaseous and vaporous effiuents are able to leave the retort essentially undiluted by extraneous fluids except for any water or steam vapor added to prevent or retard carbonization, or to sweep product vapors from the solids, or for other reasons to the retort or effluent collection chamber. In a rotating retort system, the mixture movement is continuous and is aided by the action or design of the retort and by continuous withdrawing of pellets and spent shale from the exit end of the retort zone. If a rotating retort zone is used, caking or coking together of the heat-carrying pellets or spent shale will be kept low. Moreover, a rotating type of retort zone is especially suited to varying the residence time, that is, the length of time that the shale and pellets remain in the retort zone by allowing variations in pellet-to-shale ratio and volume of shale throughput. As previously indicated, greater than normal leeway in control over these variables is especially advantageous to regulation of the amount of deposition deposited on the pellets during the retorting stage of the process. The residence time for the pellets required to effect retorting and deposition of the pellet deposition is on the order of about 3 to about 20 minutes with residence times of less than 12 minutes for the pellets being preferred. The shale residence time depends on its flow or movement characteristics, and since the shale is not uniform in size and shape, the shale residence time varies.

The mixture of pellets and spent shale exits from retort zone 13 at a temperature between 800 F. and 1150 F. by way of retort exit 17 into separation zone 19 for separation of the vapor, pellets, and spent shale. The separation zone may be any sort of exiting and separation system accomplishing the functions hereinafter mentioned and may be comprised of any number of units of equipment for separating and recovering one or more of these three classes of retort zone effiuents either simultaneously, or in combination, or individually. In the process of this invention, it is critical that at least 75 percent of the total spent shale be separated from the pellets in the separation zone to eventually be collected in separation zone exit line 21. In addition, at least 95 percent of the spent shale smaller than the pellets is separated. As shown in FIG. 2, the retort zone mixture is first passed through revolving screen or trommel 23 which has openings or apertures sized to pass the pellets and spent shale of the same or smaller size than the pellets. The trommel extends into product recovery chamber 25. In the trommel, the gaseous and vaporous products separate from the mixture of pellets and spent shale and, at the same time, at least a portion of the larger spent shale particles or agglomerates are separated from the pellets and spent shale. Most of the spent shale and pellets flow through the openings in trommel 23 and drop to the bottom of recovery chamber 25 to exit via retort exit line 27. Any spent shale or agglomerates too large to pass through the openings in the trommel pass outward through exit 29. The product vapors and gases resulting from retorting the oil shale collect overhead in recovery chamber 25 and rapidly pass to overhead retort products line 3-1 at an exit temperature between about 750 F. and 1050 F. where the product vapors may or may not be divided into two streams either before or after the vapors are subjected either in their vaporous or condensed or partially condensed state to hot dust separation (not shown) and/r fractionation or partial fractionation (not shown), and/ or other stages :(not shown) of the overall operation. The hot dust separation may be interior or exterior, or both, of recovery chamber 25 and the dust thus collected may be combined and handled with other spent shale. Hot dust or fines separation may be accomplished by hot gas cyclones, quenching and washing, agglomeration with sludge or a separately condensed heavy product fraction, centrifuging, filtration, or the like. Partial fractionation may be accomplished by condensing only a high boiling fraction of the vapors, e.g. 900 F.+ materials.

Regardless of whether any such additional processing step is taken, at least a part of the product oil collected in overhead line 31 is eventually passed through supplemental deposition feed line 33 to supplemental deposition unit 35 where a postpyrolysis combustible deposition is formed on at least a portion of the pellets from the retort zone and which will be hereinafter described. For simplicitys sake, feed line 33 is shown directly connected through a metering valve and feed pump 37 to overhead line 31 in a way which allows all or a part of the product to be fed to supplemental deposition unit 35.

As mentioned previously, the gases are not diluted by other gases and are, therefore, readily used in the overall shale operation. Some gas may be needed for supplementary fuel and some for production in the usual manner of hydrogen if hydrogenation is used in the overall shale operation. The optimum amount of gas production is just enough to satisfy these requirements as this process stresses the liquid oil products produced in the overall shale operation.

As shown in FIG. 2, the spent shale and pellets in recovery chamber 25 are discharged via exit line 27 at a temperature between about 750 F. and 1050 F. where these particulate solids are passed or conducted by gravity or other means of conveyance to gas elutriation system 39 which is a part of separation zone 19. In the elutriation system, a major portion, and more preferably substantially all, of the remaining spent shale is separated from the pellets. It is essential that elutriation be accomplished in a way which retains the desired amount of carbon-containing deposition on the pellets; consequently, the elutriating gas fed by line 41 is a noncombustion supporting gas. By conducting the process with pellets in the size range between about 0.055 and 0.5 inch, and preferably between 0.055 and 0.375 inch, at least 75 percent of the total spent shale may be separated by action of the trommel and subsequent gas elutriation at a velocity of between 18 and 25 feet per second if most of the raw shale feedstock was crushed to about minus three-fourths inch.

Based on an average of six sieve analyses of spent shale produced by retorting of one-half inch shale feedstock in a rotating retort using ceramic one-half inch balls, about 16 percent by weight (analyses range 8% to 27%) of the spent shale is retained on a US. Sieve Series size 14 screen which is in a size range similar to the pellets. Gas elutriation with irregular or cylindrical shaped pellets only separates about 2.0 to 4.0 percent of this portion of the spent shale from the pellets. Therefore, on an average between 12 and 13 percent of the spent shale is diifcult to separate by screening and elutriation depending on whether the pellets cover the entire size range of this part of the spent shale. As mentioned previously, retention of more than 25 percent of the spent shale interferes with proper operation of the pellet deposition burning zone even if most of the spent shale entering the burning zone is originally in the same size range as the pellets. Upon combustion, this spent shale would disintegrate further to fine ash and cause erratic operation of the combustion zone. Separation of the spent sha e prior to the supplemental deposition stage of this process is also desirable. Otherwise, some of the combustible deposition would be deposited on the spent shale. In addition, some allowance is made for spent shale and ash buildup as the pellets are cycled and recycled through the process.

Since the spent shale having a size similar to the pellets is diflicult to elutriate while the spent shale smaller than the pellets is readily separated by elutriation, and practically complete, it is desirable to alter the characteristics of the spent shale or of the pellets to accomplish a greater degree of separation while holding heat losses in the pellets to a reasonable level. One way to accomplish this objective is to crush at least percent by weight of the shale feedstock to a minus 6 screen size. This results in a separation of at least 95 percent by weight of the total spent shale from the pellets and the trommel may also be eliminated. As mentioned previously, crushing to this size is costly and normally not done; however, in view of the fact that in this invention it is essential that the bulk of the spent shale be separated from the pellets prior to reheating of the pellets, the cost of additional crushing may be justified. Another way to accomplish the objective of this separation prior to reheating the pellets has been discovered. It has been found that if the pellets are essentially spherical, that is, have a sphericity factor of at least 0.9, the efficiently of separation by gas elutriation is greatly increased when the raw shale is crushed to a minus three-fourths size. Spherical pellets have improved flow properties over spent shale and for a given screen size particles exhibit greater weight per particle. Gas elutriation with spherical pellets will separate about 97 percent or more of the spent shale retained on a US. Sieve Series size 14 screen and will provide almost complete separation of the smaller spent shale. Thus, if spherical pellets are used, gas elutriation will separate at least 95 percent of the spent shale in the separation zone. As mentioned previously, therefore, the preferred shape of the pellets is spherical, that is, the preferred pellet should have a sphericity factor of at least 0.9.

The separated spent shale is carried out of the elutriating chamber overhead through line 43. The spent shale is collected and may be combined and handled with other spent shale for eventual compaction and waste disposal or sale for use in manufacturing other products.

As previously mentioned, at least a portion of the separated pellets with the combustible deposition previously deposited on the pellets and at least a portion of the oil products originally produced in the retort zone are fed or passed to supplemental deposition zone 35. When the oil products contact the pellets, some of the oil is absorbed on the pellets and some of the oil is stabilized and cracked to upgrade the oil and the resulting coke-like deposition is deposited as useful fuel material for heating the pellets. In both events, additional combustible deposition is deposited on the pellets; however,

the absorbed oil may later be stripped from the pellets since it is common practice to sweep products from particles used in a cracking unit. Thus, the supplemental deposition zone provides flexibility and adaptability in regulating the total amount of combustible deposition formed on the pellets during the process by adding to the combustible deposition formed on the pellets during earlier stages of the process. This in turn allows more leeway in operating the retort zone.

Accordingly, as illustrated in the drawings, the separated pellets pass from the separation zone via separation zone exit line 45 either by way of supplemental deposition zone feed line 47 to supplemental deposition zone 35 or bypass the supplemental deposition zone by way of bypass line 49 directly to pellet return line 51. At the same time, at least a portion of the oil products originally produced in the retort zone are fed or passed by way of product feed line 33 to supplemental deposition zone 35 where the products in the usual reactor manner pass over and into contact with the pellets fed to the zone. The oil products passed to the supplemental deposition zone may if desired be preheated by indirect heat exchange located either outside or inside the supplemental deposition zone. Generally, it is best to preheat the oil products if the products are substantially cooler than the pellets. For example, the oil products may have been derived from a fractionating unit.

The temperature of the pellets entering the supple.- mental deposition zone depends on the exiting temperature of the pellets as they leave the retort zone, that is, 800 F. to 1050 F., and heat losses or additions occurring during travel of the pellets from the retort zone to overall retorting process. An oil feed has a boiling point range between 100 F. and 700 P. if at least 90 percent of the feed has a boiling point within this range. Narrower oil. cuts within this range may be selected.

As mentioned previously, it is highly desirable that the supplemental deposition zone be operated under conditions such that the oil products fed to the zone undergo significant thermal stabilization and some thermal cracking so that the deposition formed in the supplemental deposition zone will be comprised essentially of coke-like products. This limits product losses for fuel on the pellets to coke-like residue-s and at the same time provides additional stabilization and upgrading of the selected products. Oil feed with above-mentioned preferred boiling point range are especially useful for this purpose. Moreover, under thermal cracking or thermal stabilization conditions, the space velocity may be varied to control the amount of combustible deposition formed on the pellets passed to the supplemental deposition zone and on the degree of cracking and stabilization of the oil products treated. The space velocity is herein defined as the ratio of the pounds of oil products passed to the supplemental deposition zone per hour to the pounds of pellets in the supplemental deposition zone. As shown in Table 4, when a composite naphtha oil fraction from a ball type of oil shale retort with a selected boiling range between 100 F. and 700 F. was thermally treated at 900 F., small incremental changes in space velocities from 2.5 to 0.25 and lower cause a substantial change in the amount of carbon deposited on the pellets passed to the supplemental deposition zone. With less desirable higher boiling oil feeds, even lower space velocities must be used.

TABLE 4.THERMAL TREATMENT OF COMPOSITE NAPHTHA AT 900 F.

1 Pellet holding time was 30 minutes. 2 Values are approximate values. 3 Values for 0.25 space velocity are extrapolated values.

the supplemental deposition zone, especially during passage of the pellets through the separation zone. The amount, effective surface area, and temperature of the pellets and the amount and nature of the oil products passed to the supplemental deposit-ion zone primarily determine the amount of combustible deposition formed in the supplemental deposition zone unless additional heat is added to the zone. Other factors affecting the amount and nature of the deposition are the average supplemental deposition zone temperature, the space velocity, and the pellet holding time. For practical reasons, when a system has one been placed in operation, control over the system is maintained by the oil product feed rate, the pellet rate, or both. It is usually uneconomical to attempt to change the pellet temperature, the nature of the oil feed, the pellet surface area, and the like. The net surface area of the pellets will, of course, change with changes in the richness of the oil shale changes since a coke-like deposition is formed in the retort zone. Originally, the nature of the oil feed can be preset by fractionating the retort zone oil products; but generally, once a fractionating unit is in operation, it is undesirable to attempt to change the nature of the oil feed by changing the fractionating unit.

It has been discovered that a preferred feed for the supplemental deposition zone is the portion of the retort zone products within the boiling point range between 100 F. and 700 F. Higher boiling point feeds tend to create problems, and reduce flexibility and reliability of use of the supplemental deposition as a control over the As illustrated by Table 4, the cumulative weight percent at different endpoint boiling points of the cracked, stabilized product from the supplemental deposition zone shows that as the space velocity is decreased the oil fraction undergoes a greater degree of cracking and stabilization. The maleic anhydride number is a standard test used to indicate conjugate diolefins which in turn is an indicator of the degree of stabilization of the thermally treated product. Since the maleic anhydride number is the milligrams reacted per gram of feed, a decrease in maleic anhydride number indicates a greater degree of stabilization. As the space velocity decreases the product treated in the supplemental deposition zone is made more stable.

As a result, some of the products fed to the supplemental deposition zone are either cracked or adsorbed, or both. The balance of the treated product, which is preferably thermally cracked and stabilized, is then passed to supplemental deposition zone product exit line 53. The pellets in turn pass by gravity or other mechanical means through supplemental deposition zone pellet exit line 55 to pellet return line 51 where, as hereafter shown, they are carried to a pellet deposition burning zone. The amount of combustible deposition deposited on the pellets during the supplemental deposition or thermal stabilization stage should be less than five percent by weight of the pellets passed through the supplemental deposition zone. This avoids local overheating of the treated pellets and localized hot spots in the pellet deposition burning zone when, as hereafter described, the combustible deposition on the pellets is burned.

The pellets in pellet return line 51 pass to pellet lifting system 57 where the pellets are lifted preferably to an elevation which allows gravity feed to retort zone 13 by way of lift line 59 to pellet deposition burning zone 61, which as shown in FIG. 2 has surge hopper 63 for collecting the lifted pellets and leveling out fluctuations and from which the pellets fall into pellet deposition burning zone 65. While any conveying and lifting system holding heat losses to a reasonable value may be used, it is preferred as shown in FIG. 2 that the pellet lifting system be a pneumatic conveying system which will operate in the conventional manner to lift the pellets to the pellet deposition burning zone. The lift gas enters the lift system via line 67 at a velocity between 25 and 70 feet per second and the lift time is, therefore, very short. As a result, air may be used as the lift gas without causing uncontrolled combustion of the deposition on the pellets and the detrimental effects attendant to such uncontrolled burning.

As mentioned previously, the pellets bear a combustible deposition which was absorbed or deposited during the process. This combustible deposition is burned in combustion or pellet deposition burning zone 65 to provide at least 50 percent or more of the heat required to reheat the pellets to the temperature required to effect retorting of the shale. The combustible deposition is burned in a manner similar to the way that catalytic cracking catalysts particles are regenerated and which is controlled to avoid excessive heating of the pellets which would excessively reduce the effective surface area of the pellets to less than square meters per gram. A progressive bed burner with a gas flow of about one to two feed per second is preferred. A combustion supporting gas, for example air, a mixture of air and fuel gas generated in the process, flue gas with the desired amount of free oxygen, is blown into the pellet deposition burning zone at a temperature at which the deposition on the pellets is ignited by way of combustion gas inlet 69 which in FIG. 2 includes a blower. Steam may also be used to control burning provided that the steam does not excessively reduce the surface area of the pellets. The combustion supporting gas may be preheated in heaters 71 by burning some othe gases produced in the process to reheat the pellets to the minimum ignition temperature. The quantity of combustion supporting gas, e.g. about 10 to pounds of air per pound of carbon deposit, affects the total amount of deposition burned and the heat generated by such burning and in turn the temperature of the pellets. The bulk density of the pellets is about 40 to 50 pounds per cubic foot and the specific heat of the pellets varies between about 0.2 and 0.3 British thermal units per pound per degree Fahrenheit. The gross heating value of the carbon-containing deposition is estimated to be about 15,000 to 18,000 B.t.u. per pound. The amounts of carbon dioxide and carbon monoxide produced in the flue gases created by burning the pellet deposition indicate the amount of combustion supporting gas re quired or used and the amount of carbon-containing deposit not burned. Generally, it is desirable to attempt to free the pellets of combustible deposition. In any case, at least 50 percent of the combustible deposition is burned. The unburned deposition stays with the pellets and affects to some degree the total amount of combustible deposition deposited in the next cycle. It should be noted that this type of controlled burning does not selectively burn the same amount of deposit from every pellet. Other factors taken into consideration during burning of the pellet de position are the pellet porosity, density and size, the burner chamber size and pellet bed size, residence burning time, the desired temperature for the pellets, heat losses and inputs, the pellet and shale feed rates to the retort zone and the like. The residence burning time will usually be rather long and up to about 30 to 40 minutes. Combustion of the deposition should be controlled in a manner which does not heat the pellets to above 1400 F. The hot flue gases generated in the pellet deposition burning zone may be removed by burner overhead exit'line 73 and used to preheat cool raw shale feedstock or for heat transfer to any other phase or part of the shale operation. For example, this stream could be fed to a carbon monoxide boiler and the heat available from the boiler could be used for processing product vapors or to drive turbines. Of course, additional fuel material or gases may be used to supplement burning of the pellet deposition if this is necessary, but it is to be understood that the pellet deposition supplies the major portion of the sensible heat required for retorting the oil shale and that the variables are set to accomplish this objective along with the other advantages and objectives of this process.

A continuous stream of hot pellets having a temperature above 950 F. and not exceeding 1400" F. is thereby produced for return and introduction via burner bottom exit line 75 back through pellet inlet line 15 either by gravity and/ or mechanical means into retort zone 13. As previously indicated, the rate of passage of the pellets from the combustion zone will be metered or controlled in conventional manners to eventually provide the optimum pellet-to-oil shale feedstock ratio to the retort zone. The optimum ratio is governed by the pellet properties, the surface area of the pellets as they enter the retort zone, the organic content of the raw oil shale, and the other process variables as previously described.

EXAMPLE A retort train operating at a pounds-of-pellets to pounds-of-shale ratio of 2:1 and charging pellets with an effective surface area of 46 square meters per gram processes 400 tons per hour of raw oil shale. The pellets enter the retort zone at an average of about 1300 F. and provide the heat necessary to retort raw oil shale at 450 F. A combustible deposit of 1.24 weight percent is deposited on the pellets in the retort. The pellets and processed shale exit the retort zone into a separation zone where about 98 percent of the processed shale is separated from the pellets. The pellets exit the separation zone at a temperature of about 900 F. A side slip stream of about 4.34 percent or about 69,440 pounds per hour of pellets is passed to the supplemental deposition zone. For illustration purposes, 32,000 pounds per hour of a rough naphtha oil having a simulated gas chromatography true boiling point distillation showing 35 cumulative Weight percent at 350 F., 68 cumulative weight percent at 500 F., and 94 cumulative weight percent at 600 F. is passed as an oil feed to the supplemental deposition zone. The oil feed passed to the supplemental deposition is preheated to about 900 F. The supplemental deposition zone is charged with pellets and sized to provide a holding time of about 0.5 hour. The space velocity is about 0.92. In the supplemental deposition zone an additional 2.72 percent by weight of combustible deposition is deposited on the slip stream of pellets. The rough naphtha oil feed in the illustration is thermally stabilized and cracked with an estimated reduction in maleic anhydride number of from about 21.7 to about 13.2. The treated slip stream of pellets from the supplemental deposition is recombined with the other pellets from the retort zone forming a pellet mixture containing about 1.36 weight percent of combustible deposi tion thereby increasing by about 10 percent the amount of combustible deposition that can be used as fuel in the pellet deposition burning zone.

Although the retorting process is carried out in a manner to hold loss of pellets to a minimum, some pellets will be lost in the process and a relatively small quantity of pellets may be added continuously to maintain the pellet quantity.

The foregoing description of the conditions and variables of the process illustrates a preferred method of conducting the process and how the supplemental deposition stage of the process coacts with the retorting stage to accomplish the advantages and objectives herein set forth.

Reasonable variations and modifications are practical with the scope of this disclosure without departing from the spirit and scope of the claims of this invention. For example, while the disclosure of this process and the vari ables have been limited to oil shale, the process concepts lend themselves readily to retorting any solid organic carbonaceous material containing hydrocarbon values Which can be recovered by thermal vaporization of the solid carbonaceous material, such as, for example, coal, peat, and tar sands. By way of further example, while only a single train of units and stages have been described, it is to be understood that any stage or zone could be comprised of more than one stage or zone, each of which could be operated under diiferent conditions to provide the overall combined effect set forth.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method for retorting crushed oil shale containing carbnoaceous organic matter and mineral matter wherein oil shale is retorted by contacting said oil shale with hot pellets in a retort zone to gas and oil products, a combustible deposition on said pellets, and particulate spent shale, said pellets having been heated in a pellet deposition burning zone to a retort zone inlet temperature of between 1000 F. and 1400 F. mainly by combustion of a combustible carbon-containing deposition on said pellets, said pellets being in an amount suflicient to provide at least 50 percent of the heat required to vaporize a major portion of the carbonaceous matter from said oil shale and to heat said crushed oil shale from its retort zone inlet temperature to a retort zone outlet temperature of between 800 F. and 1150 F., and wherein said gas and oil products are separated and recovered, the improvement comprising passing at least a portion of said pellets from said separation zone to a supplemental deposition zone and at the same time passing at least a portion of said oil products to said supplemental deposition zone into contact with said pellets in said supplemental deposition zone to deposit additional combustible carbon-containing deposition on said pellets in said supplemental deposition zone, and thereafter passing said pellets with said additionally deposited combustible deposition from said supplemental deposition zone to said pellet deposition burning zone.

2. The method according to claim 1 wherein said pellets are comprised of particulate solid heat carriers in a size range between approximately about 0.055 inch and 0.5 inch and have a surface area of between 10 and 150 square meters per gram of pellets, the amount of said pellets also being such that the ratio of said pellets to said crushed oil shale in said retort zone on weight basis is between one and three, and wherein at least 75 percent by weight of the total of said spent shale and at least 95 percent by weight of the portion of said spent shale that is smaller in size than said pellets is separated in a separation zone from said pellets after retorting of said oil shale but prior to said heating of said pellets by combustion of said deposition on said pellets.

3. The method according to claim 2 wherein the particulate solid heat carriers are in a size range between approximately 0.055 inch and 0.375 inch.

4. The method according to claim 1 wherein the oil products passed to said supplemental deposition zone have a boiling point range between 100 F. and 700 F. and are partially thermally cracked and stabilized to at least partially deposit said additional combustible carbon-containing deposition on said pellets in said supplemental deposition zone.

5. The method according to claim 4 wherein said pellets are comprised of particulate solid heat carriers in a size range between approximately about 0.055 inch and 0.5 inch and have a surface area of between 10 and 15 square meters per gram of pellets, the amount of said pellets also being such that the ratio of said pellets to said crushed oil shale in said retort zone on weight basis is between one and three, and wherein at least 75 percent by weight of the total of said spent shale and at least percent by weight of the portion of said spent shale that is smaller in size than said pellets is separated in a separation zone from said pellets after retorting of said oil shale but prior to said heating of said pellets by combustion of said deposition on said pellets.

6. The method according to claim 5 wherein the particulate solid heat carriers are in a size range between approximately 0.055 inch and 0.375 inch.

7. A method for retorting of crushed oil shale containing carbonaceous organic matter and mineral matter comprising (a) feeding crushed oil shale and pellets to a retort zone, said pellets being comprised chiefly of particulate heat carriers being in a size range between 0.5 inch and approximately about 0.055 inch and having a surface area of between 10 and 150 square meters per gram of pellets, said pellets being at a retort zone inlet temperature between 1000 F. and 1400" F. and in a quantity such that the ratio of said heatcarrying pellets to said crushed oil shale entering said retort zone on a weight basis is between one and three, said ratio also being such that the sensible heat in said pellets is suflicient to provide at least 50 percent of the heat required to heat said crushed oil shale from its retort zone feed temperature to a retort zone outlet temperature of between 800 F. and 1150 F.;

(b) retorting in said retort zone gas and oil products from said crushed oil shale, thereby forming particulate spent shale and a combustible carbon-containing deposition on said pellets;

(c) causing said pellets and said spent shale to pass from said retort zone to a particle separation zone and separating from said pellets at least 75 percent by weight of the total spent shale and at least 95 percent by weight of the portion of said spent shale that is smaller in size than said pellets, prior to heating said pellets in a pellet deposition burning zone;

(d) recovering said gas and oil products generated by retorting of said crushed oil shale;

(e) passing at least a portion of said pellets from said separation zone to a supplemental deposition zone and at the same time passing at least a portion of said oil products to said supplemental deposition zone into contact with said pellets in said supplemental deposition zone to deposit additional combustible carbon-containing deposition on said pellets in said supplemental deposition zone;

(f) passing said pellets bearing said additional combustible carbon-containing deposition from said supplemental deposition zone to a pellet deposition burning zone;

(g) heating said pellets in said pellet deposition burning zone to an outlet temperature of between 1000 F. and 1400 F. by burning the combustible carboncontaining deposition on said pellets with a combustion supporting gas; and

(h) thereafter passing said heated pellets from said pellet deposition burning zone to said retort zone.

8. The method according to claim 7 wherein the particulate heat carriers are in a size range between 0.375 inch and approximately about 0.055 inch.

9. The method according to claim 7 wherein the average amount of said combustible deposition formed on said pellets upon passage through said retort zone is on said average less than 1.5 percent by weight of said pellets.

10. The method according to claim 7 wherein in step (e) the oil products passed to said supplemental deposition zone have a boiling range between F. and 700 F. and are partially thermally cracked and stabilized to at least partially deposit said additional combustible carbon-containing deposition on said pellets in said supplemental deposition zone.

11. The method according to claim 10 wherein the particulate heat carriers are in a size range between 0.375 inch and approximately about 0.055 inch.

12. The method according to claim 10 wherein the average amount of said additional combustible deposi tion formed on said pellets in said supplemental deposition zone is on said average less than percent by weight of said pellets passed through said supplemental deposition zone.

13. The method according to claim wherein in step (e) the ratio of the pounds of oil products passed to said supplemental deposition zone per hour to the pounds of pellets in said supplemental deposition zone is less than 2.5.

14. The method according to claim 10 wherein the average amount of said combustible deposition formed on said pellets upon passage through said retort zone is on said average less than 1.5 percent by weight of said pellets.

15. The method according to claim 14 wherein the average amount of said additional combustible deposition formed on said pellets in said supplemental deposition zone is on said average less than 5 percent by weight of said pellets passed through said supplemental deposition zone.

16. The method according to claim 14 wherein in step (e) the ratio of the pounds of oil products passed to said supplemental deposition zone per hour to the pounds of pellets in said supplemental deposition zone is less than 2.5.

17. The method according to claim 7 wherein the separation of step (c) is comprised of first passing said pellets and said spent shale through apertures in a trommel to screen out at least a portion of the spent shale and any agglomerates larger than said pellets, and thereafter subjecting the remaining pellets and spent shale to gas elutriation with a noncombustion supporting gas to etfeet further separation of the spent shale from the pellets.

18. The method according to claim 17 wherein the average amount of said combustible deposition formed on said pellets upon passage through said retort zone is on said average less than 1.5 percent by weight of said pellets.

19. The method according to claim 17 wherein in step (e) the oil products passed to said supplemental deposi tion zone have a boiling point range between 100 F. and 700 F. and are partially thermally cracked and stabilized to at least partially deposit said additional combustible carbon-containing deposition on said pellets in said supplemental deposition zone.

20. The method according to claim 19 wherein the particulate heat carriers are in a size range between 0.375 inch and approximately about 0.055 inch.

21. The method according to claim 19 wherein the average amount of said additional combustible deposition formed on said pellets in said supplemental deposition zone is on said average less than 5 percent by weight of said pellets passed through said supplemental deposition zone.

22. The method according to claim 19 wherein in step (e) the ratio of the pounds of oil products passed to said supplemental deposition zone per hour to the pounds of pellets in said supplemental deposition zone is less than 2.5.

23. The method according to claim 19 wherein the average amount of said combustible deposition formed on said pellets upon passage through said retort zone is on said average less than 1.5 percent by weight of said pellets.

24. The method according to claim 23 wherein the average amount of said additional combustible deposition formed on said pellets in said supplemental deposition zone is on said average less than 5 percent by weight 20 I of said pellets passed through said supplemental deposition zone.

25. The method according to claim 23 wherein in step (e) the ratio of the pounds of oil products passed to said supplemental deposition zone per hour to the pounds of pellets in said supplemental deposition zone is less than 2.5.

26. The method according to claim 7 wherein the pellets have a sphericity factor of at least 0.9 and at least percent by weight of the total spent shale is separated from said pellets in step (c).

27. The method according to claim 26 wherein the average amount of said combustible deposition formed on said pellets upon passage through said retort zone is on said average less than 1.5 percent by weight of said pellets.

28. The method according to claim 26 wherein in step (e) the oil products passed to said supplemental deposition zone have a boiling point range between F. and 700 F. and are partially thermally cracked and stabilized to at least partially deposit said additional combustible carbon-containing deposition on said pellets in said supplemental deposition zone.

29. The method according to claim 28 wherein the particulate heat carriers are in a size range between 0.375 inch and approximately about 0.055 inch.

30. The method according to claim 28 wherein the average amount of said additional combustible deposition formed on said pellets in said supplemental deposition zone is on said average less than 5 percent by weight of said pellets passed through said supplemental deposition zone.

31. The method according to claim 23 wherein in step (e) the ratio of the pounds of oil products passed to said supplemental deposition zone per hour to the pounds of pellets in said supplemental deposition zone is less than 2.5.

32. The method according to claim 28 wherein the average amount of said combustible deposition formed on said pellets upon passage through said retort zone is on said average less than 1.5 percent by weight of said pellets.

33. The method according to claim 32 wherein the average amount of said additional combustible deposition formed on said pellets in said supplemental deposition zone is on said average less than 5 percent by weight of said pellets passed through said supplemental deposition zone.

34. The method according to claim 32 wherein in step (e) the ratio of the pounds of oil products passed to said supplemental deposition zone per hour to the pounds of gesllets in said supplemental deposition zone is less than 35. The method according to claim 7 wherein at least 95 percent by weight of the crushed oil shale of step (a) has been crushed to a size to pass through a US. Sieve Series size 6 screen and at least 95 percent by weight of the total spent shale is separated from said pellets in step (c).

36. The method according to claim 35 wherein the average amount of said combustible deposition formed on said pellets upon passage through said retort zone is on said average less than 1.5 percent by Weight of said pellets.

37. The method according to claim 35 wherein in step (e) the oil products passed to said supplemental deposition zone have a boiling point range between 100 F. and 700 F. and are partially thermally cracked and stabilized to at least partially deposit said additional com bustible carbon-containing deposition on said pellets in said supplemental deposition zone.

38. The method according to claim 37 wherein the particulate heat carriers are in a size range between 0.3 75 inch and approximately about 0.05 5 inch.

39. The method according to claim 37 wherein the average amount of said additional combustible deposition formed on said pellets in said supplemental deposi- 21 tion zone is on said average less than 5 percent by weight of said pellets passed through said supplemental deposition zone.

40. The method according to claim 37 wherein in step (e) the ratio of the pounds of oil products passed to said supplemental deposition zone per hour to the pounds of pellets in said supplemental deposition zone is less than 2.5.

41. The method according to claim 37 wherein the average amount of said combustible deposition formed on said pellets upon passage through said retort zone is on said average less than 1.5 percent by Weight of said pellets.

42. The method according to claim 41 wherein the average amount of said additional combustible deposition formed on said pellets in said supplemental deposition zone is on said average less than 5 percent by weight of said pellets passed through said supplemental deposition zone.

UNITED STATES PATENTS 3,008,894 11/1961 Calbertson 208-11 3,018,243 1/1962 Nevens 20811 3,020,227 2/ 1962 Nevens et a1 20811 3,058,903 10/1962 Otis 20811 3,252,886 5/1966 Crawford 20811 3,573,197 3/1971 Gessner 20811 3,803,021 4/ 1974 Abdul-Rahman 20811 3,803,022 4/1974 Abdul-Rahman 20811 CURTIS R. DAVIS, Primary Examiner 

1. IN A METHOD FOR RETORTING CRUSHED OIL SHALE CONTAINING CARBONACEOUS ORGANIC MATTER AND MINERAL MATTER WHEREIN OIL SHALE IS RETORTED BY CONTACTING SAID OIL SHALE WITH HOT PELLETS IN A RETORT ZONE TO GAS AND OIL PRODUCTS, A COMBUSTIBLE DEPOSITION ON SAID PELLETS, AND PARTICULATE SPENT SHALE, SAID PELLETS HAVING BEEN HEATED IN A PELLET DEPOSITION BURNING ZONE TO A RETORT ZONE INLET TEMPERATURE OF BETWEEN 1000*F. AND 1400*F. MAINLY BY COMBUSTION OF A COMBUSTIBLE CARBON-CONTAINING DEPOSITION ON SAID PELLETS, SAID PELLETS BEING IN AN AMOUNT SUFFICIENT TO PROVIDE AT LEAST 50 PERCENT OF THE HEAT REQUIRED TO VAPORIZE A MAJOR PORTION OF THE CARBONACEOUS MATTER FROM SAID OIL SHALE AND TO HEAT SAID CRUSHED OIL SHALE FROM ITS RETORT ZONE INLET TEMPERATURE TO A RETORT ZONE OUTLET TEMPERATURE OF BETWEEN 800*F. AND 1150*F. AND WHEREIN SAID GAS AND OIL PRODUCTS ARE SEPARATED AND RECOVERED, THE IMPROVEMENT COMPRISING PASSING AT LEAST A PORTION OF SAID PELLETS FROM SAID SEPARATION ZONE TO A SUPPLEMENTAL DEPOSITION ZONE AND AT THE SAME TIME PASSING AT LEAST A PORTION OF SAID OIL PRODUCTS TO SAID SUPPLEMENTAL DEPOSITION ZONE INTO CONTACT WITH SAID PELLETS IN SAID SUPPLEMENTAL DEPOSITION ZONE TO DEPOSIT ADDITIONAL COMBUSTIBLE CARBON-CONTAINING DEPOSITION ON SAID PELLETS IN SAID SUPPLEMENTAL DEPOSITION ZONE, AND THEREAFTER PASSING SAID PELLETS WITH SAID ADDITIONALLY DEPOSITED COMBUSTIBLE DEPOSITION FROM SAID SUP PLEMENTAL DEPOSITION ZONE TO AID PELLET DEPOSITION BURNING ZONE. 